1. Field of the Invention
The present invention relates to an output control device for an optical pick-up (optical head) used in an optical disc drive and a method for controlling output of the optical pick-up.
2. Description of the Related Art
There are known optical disc drives for reproducing (playing back) a read only optical disc such as a CD-ROM, and for recording and reproducing a recordable optical disc such as CD-R and CD-RW.
Such an optical disc drive has an optical pick-up which is movable in the radial direction of the optical disc, and an optical pick-up moving mechanism equipped with a sled motor for moving the optical pick-up in the radial direction of the optical disc.
The optical pick-up is constructed from an optical pick-up main body (an optical pick-up base) which is equipped with a laser diode, a split photodiode and an I-V amplifier, an objective lens supported by the optical pick-up main body with suspension springs so as to be movable in the radial direction as well as in the rotational axis direction of the optical disc, and an actuator for moving the objective lens in the radial direction and in the rotational axis direction of the optical disc.
In such an optical disc drive, recording of data to the optical disc and reproduction (read-out) of data from the optical disc are carried out for a predetermined track while performing focus control, tracking control and the like.
FIG. 11 is a circuit diagram which shows a split photodiode and I-V amplifiers used in a conventional optical disc drive. As shown in the drawing, a split photodiode 110 is electrically connected to each of I-V amplifiers 121, 122, 123, 124, 125 and 126, respectively.
For recording and reproducing an optical disc, a laser beam is projected toward the optical disc from a laser diode (which are not shown in the drawing).
In this case, when the data is to be reproduced from the optical disc, the output level of the laser beam projected toward the optical disc is set to a reproduction level, and the quantity of reflected light from the optical disc goes to a low level.
On the other hand, when the data is to be written onto the optical disc by forming pits and lands, the output level of the laser beam is controlled as follows. Namely, when the pits are to be formed, the output level of the laser beam is raised to a recording level (about 10 to 30 times the reproduction level), and the quantity of reflected light from the optical disc goes to a high level. On the other hand, when no pits are to be formed (that is, when lands are to be formed), the output level of the laser beam is lowered to the reproduction level, and the quantity of reflected light from the optical disc goes to the low level.
The reflected light from the optical disc (laser beams) is received by light receiving regions 111, 112, 113, 114, 115, and 116 of the split photodiode 110, and currents corresponding to the quantities of received light at respective regions 111 to 116 of the split photodiode 110 are outputted.
The currents from the split photodiode 110 are amplified with predetermined amplification factors and converted into voltages by the respective I-V amplifiers 121, 122, 123, 124, 125 and 126, and then inputted into predetermined post stage circuits.
In the case of an optical disc drive which is capable of only performing reproduction of an optical disc, since the output level of the laser beam projected to the optical disc is constant (at the reproduction level) as mentioned above, variations in the currents from the split photodiode 110 are relatively small.
On the other hand, however, in the case of an optical disc drive which is capable of performing both of recording and reproduction of an optical disc, the output level of the laser beam projected to the optical disc when recording is being carried out is about 10 to 30 times that of reproduction as mentioned above. Therefore, there may arise a problem that the dynamic ranges of the I-V amplifiers are insufficient to deal with the currents.
In other words, in the case of an optical disc drive capable of performing both of recording and reproduction, if the amplification factor of respective I-V amplifier is set at a relatively high value so as to be suitable for reproduction and then a current is converted into a voltage for recording by the I-V amplifier having such a setting, the high voltage side of the voltage waveform is likely to be truncated, which may give rise to a situation in which the correct voltage corresponding to the received quantity of light is not obtained. This may also cause an inconvenience in various controls that are to be carried out in the recording operation.
On the other hand, if the amplification factor of the I-V amplifier is set at a relatively low value suitable for recording, the voltage (signal level) outputted from the I-V amplifier becomes too low at reproduction. This may case an inconvenience in various controls that are to be carried out in the re producing operation.
These problems may be resolved by using an I-V amplifier with a relatively wide dynamic range, but it also has certain restrictions.
Accordingly, it is an object of the present invention to provide an output control device for an optical pick-up which is capable of properly performing recording (including control for recording) and reproduction (including control for reproduction) in an optical disc drive.
In order to achieve the object, the present invention is directed to an output control device for an optical pick-up used in an optical disc drive for recording and reproducing an optical disc, in which the optical pick-up being adapted to project light having a quantity of light of either high level or low level to the optical disc. The output control device comprises light receiving means having a plurality of light receiving regions for receiving reflected light from the optical disc and then outputting electrical currents responsive to the quantity of light received at the respective light receiving regions; current-voltage converting means having a first current-voltage converting section for converting the currents supplied from the light receiving means into voltages through a predetermined amplification factor; and current supply changeover means which functions so as not to supply the currents from the light receiving means to the first current-voltage converting section when the quantity of the reflected light from the optical disc is in the high level.
In the present invention, it is preferred that the current-voltage converting means further comprises a second current-voltage converting section for converting at least a part of the currents supplied from the light receiving means into voltages through a predetermined amplification factor which is lower than that of the first current-voltage converting section, and the current supply changeover means is adapted to supply the part of the currents from the light receiving means to the second current-voltage converting section of the current-voltage converting means when the quantity of the reflected light from the optical disc is in the high level.
According to the output control device for the optical pick-up described above, since a part of the currents from the light receiving means is supplied to the second current-voltage converting section of the current-voltage converting means when the quantity of the reflected light from the optical disc is in the high level, it is possible to prevent insufficiency in the dynamic range of the current-voltage converting means.
In particular, a voltage (signal) with a relatively high level and correctly responsive to the quantity of received light at the light receiving region can be obtained, thereby enabling to perform various controls securely and reliably during the recording and reproduction operations.
In the present invention, it is also preferred that the current supply changeover means comprises main paths for supplying the currents from the light receiving means to the first current-voltage converting means; branch paths which are respectively branched from the main paths at branch portions for supplying the currents from the light receiving means to a part other than the first current-voltage converting section; and selection means for selecting either of the main paths or the branch paths to which the currents from the light receiving means are to be supplied, wherein the selection is made by the selection means so as to supply the currents from the light receiving means to the main paths when the quantity of reflected light from the optical disc is in the low level or so as to supply the currents from the light receiving means to the branch paths when the quantity of reflected light from the optical disc is in the high level.
According to the above configuration, when the output level of the laser beam is at the reproduction level, that is, when the quantity of reflected light from the optical disc is at the low level, the currents from the light receiving means such as a split photodiode flow in the main paths. On the other hand, when the output level of the laser beam is at the recording level, that is, when the quantity of reflected light from the optical disc is at the high level, the currents flow in the branch paths branched from the main paths via branch points. Therefore, it is possible to avoid the situation in which the dynamic ranges of the first current-voltage converting circuits are insufficiently narrow.
Further, it is more preferable that the branch paths include a first path connected to the second current-voltage converting section and a second path connected to a part other than the first and second current-voltage converting sections, and the currents from the light receiving means corresponding to the main beam reflected from the optical disc are adapted to be supplied to the second current-voltage convert in section through the first path when the quantity of light reflected from the optical disc is in the high level.
Furthermore, it is also preferred that the currents from the light receiving means corresponding to the sub-beams reflected from the optical disc are adapted to be outputted from the current-voltage converting means through the second path without passing through the first and second current-voltage converting sections.
In the present invention, it is preferred that the selection means is constructed from a plurality of switches, and each of the switches is provided at each of the branch portions for selectively switching between the conducting state of the light receiving means and each of the main paths at the respective branch portions and the conducting state of the light receiving means and each of the branch paths at the respective branch portions.
Further, it is also preferred that the output control device further comprises a sample-and-hold circuit for holding voltages from the first current-voltage converting section when the quantity of light reflected from the optical disc is in the high level.
When such a sample-and-hold circuit which is capable of holding the voltages from the first current-voltage converting section is provided, it is possible to more surely and reliably perform the controls during the recording and reproduction operations.
Furthermore, in the present invention, it is also preferred that the light receiving means, the current-voltage converting means and the current supply changeover means are integrally formed into a single unit. In this case, the number of part items can be reduced, and hence its assembly to the optical disc drive 1 can be facilitated.
Another aspect of the present invention is directed to a method for controlling output of an optical pick-up used in an optical disc drive for recording and reproducing an optical disc, the optical pick-up being adapted to project light having a quantity of light of either high level or low level to the optical disc. The method comprises the steps of: receiving light reflected from the optical disc by light receiving means having a plurality of light receiving regions and then outputting electrical currents responsive to the quantity of reflected light at the respective light receiving regions; and supplying the currents from the light receiving means to a first current-voltage converting section having a predetermined amplification factor when the quantity of light reflected from the optical disc is in the low level, while supplying the currents from the light receiving means to a second current-voltage converting section having a predetermined amplification facto which is lower than that of the first current-voltage converting section without supplying them to the first current-voltage converting section when the quantity of light reflected from the optical disc is in the high level.
In this method, it is preferred that the currents from the light receiving means are supplied to the first current-voltage converting section when lands are to be formed during recording to the optical disc, while the currents from the light receiving means are supplied to the second current-voltage converting section without supplying them to the first current-voltage converting section when pits are to be formed during the recording to the optical disc.
In this case, it is preferred that the currents from the light receiving means corresponding to the main beam reflected from the optical disc are adapted to be supplied to the second current-voltage converting section when the quantity of light reflected from the optical disc is in the high level. Further, it is more preferable that the currents from the light receiving means corresponding to the sub-beams reflected from the optical disc are adapted to be outputted from the current-voltage converting means without passing through the first and second current-voltage converting sections.
Other objects, structures and results of the present invention will be apparent when the following description of the preferred embodiments are considered taken in conjunction with the accompanying drawings.